Recombinant proteins are currently used to treat a number of human disorders including diabetes, neutropenia, anemia, and musculoskeletal disorders of the elderly. For example, skeletal muscle atrophy and bone wasting associated with aging can be attenuated using growth hormone (GH) and insulin-like growth factor-1 (IGF-1). For cardiovascular disorders such as heart failure and ischemia, GH, IGF-1, and vascular endothelial growth factor (VEGF) are under investigation. Delivery of proteins by daily injection is problematic in many instances since they degrade rapidly in vivo, are expensive to manufacture, and have detrimental side effects when delivered at pharmacological doses. Cell based delivery of proteins from genetically-modified implanted cells may provide a more effective and cost-saving alterative. The long-term objective of this project is to develop and optimize delivery of soluble therapeutic proteins from tissue engineered BioArtificial Muscle (BAM) platforms. Muscle stem cells (myoblasts) can be isolated in large numbers and genetically modified to express high levels of foreign proteins. When tissue engineered in vitro into organ-like BAMs and implanted in vivo, they serve as a long-term delivery system for biologically active proteins. Advantages of this technology over currently used injected myoblasts or plasmid DNA gene therapy techniques include efficient in vitro fusion of myoblasts into BAMs, preimplantation monitoring of growth factor secretion levels, and reversibility. BAMs secreting GH and engineered from a murine C2C12 muscle cell line successfully attenuated skeletal muscle disuse atrophy when implanted subcutaneously in mice, whereas daily rhGH injections were ineffective. In the current project, primary myoblasts from inbred Fisher 344 rats will be transduced to constitutively express rhGH, IGF-1, or VEGF using retroviral expression constructs. BAMs from these primary rat myoblasts will be tissue-engineered using previously developed protocols and their morphology and foreign gene expression levels evaluated in vitro and in vivo. Rat BAM (R-BAM) myofiber survival, differentiation, innervation, and vascularization will be studied in subcutaneous and muscular sites by quantitative immunocytochemical and biochemical techniques. The biological activity of GH, IGF-1 and VEGF secreted from R-BAMs to stimulate neovascularization in an ischemic hindlimb model will be assessed in adult Fisher 344 rats. New therapeutic treatments with recombinant proteins for chronic cardiovascular disorders such as ischemia and heart failure will lead to enhanced quality of life and reduced costs in this multi-billion dollar annual U.S. health care market.